<p>Sends the given PRIORITY {@code frame}.</p>
<p>If the {@code frame} references a {@code streamId} that does not exist
(for example {@code 0}), then a new {@code streamId} will be allocated, to
support <em>unused anchor streams</em> that act as parent for other streams.</p>
@param frame the PRIORITY frame to send
@param callback the callback that gets notified when the frame has been sent
@return the new stream id generated by the PRIORITY frame, or the stream id
that it is already referencing
<p>Sends the given PRIORITY {@code frame}.</p> <p>If the {@code frame} references a {@code streamId} that does not exist (for example {@code 0}), then a new {@code streamId} will be allocated, to support <em>unused anchor streams</em> that act as parent for other streams.</p>
@param frame the PRIORITY frame to send @param callback the callback that gets notified when the frame has been sent @return the new stream id generated by the PRIORITY frame, or the stream id that it is already referencing